Indigenous people will soon be able to hear a prerecorded caution in any Aboriginal language if arrested in Western Australia under changes prompted by the case of an Indigenous man who was charged with murder despite not understanding his rights or the questions.

The announcement on Thursday by the WA police commissioner, Karl O’Callaghan, comes in response to criticism over the interviewing of murder suspect Gene Gibson, who was questioned in English despite his first language being Pintupi.

The prerecorded caution system is already used in the Northern Territory and covers every Australian Aboriginal language.

O’Callaghan said WA police would also establish a specialised unit for dealing with Aboriginal witnesses and suspects from remote communities, increase training on the rights of arrested people and suspects, and attempt to negotiate to reintroduce Indigenous language interpreting services.

Gibson, a 24-year-old Pintupi man from Kiwirrkurra, a remote Aboriginal community just on the WA side of the border in the Gibson Desert, was charged in 2012 with the murder of 21-year-old Joshua Timothy Warneke.

Warneke was killed while walking home in Broome early in the morning of 26 February, 2010. Gibson was interviewed more than two years later in Kiwirrkurra. He was not provided with an interpreter, despite English being his third or fourth language.

The charge was later downgraded to manslaughter after the judge, Stephen Hall, ruled all the interview evidence was inadmissible, finding Warneke did not understand he had a right to silence and did not understand the questions, noting “in my view it is unlikely that the admissions of the accused would have been made at all if the interview had been properly conducted”.

Gibson is currently serving a seven-and-a-half year jail sentence and will be eligible for parole in 2018.

On ThursdayO’Callaghan said twin reviews of the case by police internal affairs and the Corruption and Crime Commission (CCC) “highlighted the difficulties” of interviewing Aboriginal people whose first language was not English.

O’Callaghan said findings were made against 11 police officers after that investigation and eight had received “various forms of managerial intervention”.

Of those, three were subject to the commissioner’s loss of confidence process, which is the final warning before dismissal. Two of the three, O’Callaghan said, “had the knowledge and capacity to have done a better job”.

“They made a series of judgment calls about the ability of suspects and witnesses to understand the interview process which were wrong and reflected a lack of diligence,” he said.

“Having considered the mitigating factors, I have decided they will now be subject to disciplinary processes with penalties ranging from fines to demotion.”

A third officer, who was not part of the murder investigation, is still under review.

O’Callaghan said a report on the review of the Warneke murder investigation had been forwarded to the director of public prosecutions and the attorney general.

Material collected in the review has been forwarded to Gibson’s lawyers.

Amnesty Australia said it supported the introduction of prerecorded cautions and pushed for the re-funding of Aboriginal language interpreting services.

“Amnesty would encourage the WA government to ensure that all Aboriginal interpreter services are adequately funded and launched only after input from local Aboriginal community groups,” it said in a statement to Guardian Australia.

It also called on WA police to hold local cultural competency training in various Aboriginal communities to improve relationships between those communities and police.